The present invention relates to an apparatus and to a process for the pure preparation of particles, biological all systems, colloids and the like.
It is known that particles, molecules, etc. of different densities can be separated from one another by centrifugation in liquid density gradients. For example, density gradients of this type can be obtained by rotating, in a horizontal plane, centrifuge tubes which contain liquid layers which become stepwise and continuously more dense towards their bases. If particles, molecules, biological cells, etc. are introduced centrifugally into this gravity field, then, after the sedimentation equilibrium has been reached, individual bands result in the centrifuge tube, the bands containing the heavier particles, as well as the mroe dense regions of the density gradient, being more remote from the centre of rotation than the bands containing the lighter particles. While in centrifugation arrangements of this type the separation into individual bands succeeds well with existing centrifuges, problems arise on removal of each band in the pure form. It is known that this is because the individual bands are obtained by pipetting each of them out of the centrifuge tube which has been removed from the swing-out rotor of the arrangement. However, contamination of the individual bands due to turbulence, mixing and diffusion is unavoidable during the pipetting process.
In other known processes, the gradient with the separated bands present in the centrifuge tube is pushed out by pumping in an extremely dense liquid from the lowest point in the tube to the upper rim of the tube, and is led off from there and fractionated by means of a pressed-on funnel with tubing line. However, a process of this type is complicated and requires a costly additional device. Moreover, even in this case it is not possible completely to avoid mixing of individual bands and diffusion processes.